Although diphtheria mortality and morbidity have been gradually decreasing in most parts of the United States for the past twenty-five years, they have not been reduced to the level which it was hoped would be attained. Antitoxin, control of carriers and the Schick test were important. The discovery of toxoid added new impetus to the efforts to control this disease. It was believed that the inoculation of a large proportion of the child population would result in almost complete eradication of diphtheria.
The results obtained with the use of toxoid did not, however, approximate expectations. The present study explains to some extent this failure.
In Chicago, until 1931, three 1 cc. doses of antitoxin at weekly intervals were used for diphtheria immunization. In 1931 plain toxoid, two 1 cc. doses at weekly intervals, was employed. From 1932 to 1934 alum toxoid, two 1 cc. doses at weekly intervals, was used;